Previous Image « » Next Image Click to Enlarge Click to Enlarge Click to Enlarge

Editing Simple Compositing

Compositing is omnipresent. It would be nearly impossible to watch a Hollywood film or an hour of television and not see some sort of compositing. Some films, such as Zack Snyder's Spartan epic, 300 (2006), is nearly all compositing. But what is this technique, and how do we who have less than a Hollywood budget use it?

Compositing is the combination of two or more images to form a single final image. The six o'clock news meteorologist standing in front of a weather map is a good example. The map is not really behind this person, nor is it projected. The composite is made in the "booth," where a video engineer combines the feed of the live meteorologist with the image of the map and the icons of clouds, the sun, names of counties or towns, etc.

Another great example of common composites is lower thirds. These can be static graphic or flashy motion visuals which usually identify a person and his profession. You find them often in news programs, documentaries and sporting events such as football and baseball games. Similarly, titles in films, commercials and music videos use this graphic type of compositing.

Now, I know what you are thinking: "Ah, I get it, computer-generated effects." But not all compositing is the product of microchips. George Melies, a stage magician working in France over one hundred years ago, often gets credit for being the first compositor for moving pictures. Melies admired the works of film pioneers, the Lumière brothers, in 1895 and was inspired to combine some of his sleight-of-hand with film. His famous 16-minute, black-and-white film, A Trip to the Moon (Le voyage dans la Lune, 1902) can still be found pleasing audiences over a century later.

The basic idea behind compositing is transparency. A great analogy is t-shirt silk screening. You stretch fine-mesh cloth or screen over a wooden frame. You can press ink through this screen onto a shirt. Next you adhere a "negative" of the image you want onto the screen. It's a bit like a stencil: the negative image attached to the screen will not let ink through.

When we composite, our "frame" is the pixel dimension of our video, 720x480, 1280x720, 1440x1080, etc. The screen is usually what's called an alpha channel. Instead of using a negative, you place your still or moving image right on your "screen." The "screen," "frame" or alpha channel usually disappears completely, leaving behind your image. That image can also be something more abstract, such as fog - a tint of color which will alter our image.

The alpha channel is important, because it keeps our visible image on the correct x- and y-axis. If we have a lower third which we want to use in a documentary about school teachers, we can make a template of our lower third and switch out the names and occupations of all the teachers, administrators and students in the video. The alpha channel makes sure that this "floating" lower third is always in the same position on the screen relative to height and width. Make sense? Without this layer locking in our graphic to its correct x- and y-axis, it could float around our "frame" and be inconsistent.

There are times we need to be very conscious of this alpha channel and make sure we keep it intact. For example, when we export an image from Photoshop and import it into our editing software, we need to make sure the alpha channel is not compromised. If we create graphics, lower thirds, watermarks or any other "layer" for a composite within our editing software, we may not even be conscious of this alpha layer.

To oversimplify what we are talking about, an alpha channel is 100% transparent. Your image can be fully opaque or partially transparent, have feathered or gradient transparencies and/or many other variations, adding to the complexity of your composite. Any of this making sense? Perhaps some examples will make it clearer.

We call graphics living in the lower area of the screen - usually identifying an on-camera speaker - a lower third. If you're over forty, you may know them as Chyrons, Vidifonts or superbars (or Astons or name straps, if you speak with a British accent). Today's lower thirds, at least in broadcast news and sporting events, are usually fancy, quickly-moving motion graphics, often accompanied by sound effects. Most editing software programs have nice-looking lower-third templates or ways to make custom lower thirds, built right in their titlers. Adobe's Premiere Pro has a robust titler with many lower-third options. Some quite robust third-party titlers that make industry-quality lower thirds include Boris FX, Ulead COOL 3D and Apple's Motion. Adobe's Photoshop and After Effects are 2D and 3D still and motion graphic favorites.

A bug or watermark is usually a semi-transparent graphic icon or logo that you use to tag a video. The broadcast networks, such as NBC and ABC, first used them, but now you find them most cable channels as well. If you watch YouTube videos embedded in a non-YouTube website or blog, you'll see a YouTube bug in the lower right corner of the video.